Ventral view, left side

Cat information:
 sternomastoid (cat only � corresponds
         to the medial portion of the
         sternocleidomastoid)
 origin:  manubrium and median raphe
 insertion:  lateral half of lambdoidal ridge
          and mastoid portion of temporal bone
           as far as the mastoid process
 nerve:  spinal accessory (XI) and ventral
           rami of C1-C3
 action:  bilateral contraction depresses snout,
           unilateral contraction turns head and
           depresses snout

Anterior view, right side Anterior view of origin, right side
Lateral view of insertion, right side

Human information:
sternomastoid (cat only � corresponds
        to the medial portion of the
        sternocleidomastoid)
origin:  anterior surface of manubrium
insertion:  lateral surface of the mastoid
        process and the lateral half of the
        superior nuchal line
nerve:  spinal accessory (XI) and
        anterior rami of C2 and C3
action:  bilateral contraction leads to flexion
        of the head; unilateral contraction causes
        rotation of head to the opposite side
        and movement of head toward the ipsilateral
        shoulder

The above drawings of the origin and insertion might help visualize this information (red is the origin, blue the insertion).  Note that only the sternal portion of the origin has been shown here.  The clavicular portion of the origin will be found with the cleidomastoid information.

COPYRIGHT 2009 by William C. Johnson II
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